During recent years, much research has been devoted to the improvement of dye doped solid state materials for pulsed laser applications. We report results obtained with hybrid materials doped with many different dyes and synthesized by using the sol-gel process. The best and very promising results were obtained with the pyrromethenes and are the following: We used a linear stable cavity longitudinally pumped by a nanosecond frequency-doubled Nd:YAG laser. Conversion efficiencies of 70% were obtained with no saturation effect, at least up to 15 mJ/pulse pump energy. Output emission in excess of 10 mJ were thus obtained. We monitored the evolution of the output energy when operating the solid state dye laser at about a millijoule energy pumping level, always using the same area of the sample. The progressive dye degradation leads to a decrease of the output energy. However, we may obtain high lifetime at high repetition rate: over 500,000 pulses may be emitted at 20 Hz by the same area of the sample, before the output energy decreases to half of its initial value. Moving the sample allows us to achieve with one sample, a very stable laser emission of about one millijoule for over one month utilization. This opens the route towards routine use of such solid state dye laser systems. Yet, we are still improving the stability of the dye incorporated in the solid matrices, in particular by studying the effect of removing the oxygen from the samples
Experimental results for various type polymer lasers, pumped by different frequency doubled Nd:YAG lasers with pulse energy from 1 to 400 mJ, pulse width from 5 to 500 ns, and pulse repetition rate from 1 to 25,000 Hz, are presented. A dye laser output energy exceeding 280 mJ and an average output power of more than 12 W were demonstrated in a broad band operation mode. A total energy of 190 mJ at 560 nm in a beam divergence of less than 20 mm-mrad is achieved. A tunability over 545-685 nm wavelength range was demonstrated in a narrow band operation mode (linewidth 0.4 cm-1) with more than 30 mJ maximum energy per pulse. A stable output for more than 1 million pulses at 560 nm for motionless modified polymer element at pump fluence 0.5 J/cm2 and more than 200 million pulses for movable element at pump fluence 1 J/cm2 has been achieved.
Two different monomers containing in the same molecule the Rhodamine 6G chromophore and an allyl or a methacrylic group were synthesized. These new monomers were copolymerized with mixtures of 2-hydroxyethyl methacrylate and methyl methacrylate. The resulting solid laser samples were transversely pumped by 337-nm pulses from a N2 laser, and their lasing properties were compared with those of the corresponding model dyes dissolved in the same methacrylic copolymers. Lasing efficiencies similar to those found for Rhodamine 6G in ethanol solution under the same experimental conditions have been achieved with some of the compounds. In addition, important increases in photostability have been obtained in some of the new terpolymers: lifetimes (number of pulses that produce an 80% drop in the laser output) in excess of 20,000 shots at 2 Hz and in excess of 9,000 shots at 15 Hz have been demonstrated in static samples. By using a rotating mechanism to move the laser rod in a continuous way the laser output remains stable with no sign of degradation after 500,000 shots at 2 Hz repetition rate.
Studies of the energy scaling and beam quality improvement of a long pulse laser pumped solid state dye laser are presented. These measurements establish the state of the art for beam quality and single pulse energy of a solid state plastic dye laser.
Pyrromethene-BF2 (PM) complexes doped in modified polymethyl methacrylate were evaluated and show excellent laser efficiency and damage resistance when excited at 532 nm. The spectroscopy and laser performance of a new laser dye (PM511) is discussed with emission below 550 nm. In addition, the enhanced sensitization and dual wavelength operation of dyes doped in the solid-state are demonstrated between 550 - 650 nm.
A newly synthesized laser dye, trans-4-[P-(N-ethyl-N-hydroxyethylamino)styryl]- N-methylpyridinium tetraphenylborate (dye I), has high thermal- and photo-stability as well as strong two-photon-induced upconversion emission. Utilizing dye I doped bulk polymer rods, two-photo pumped frequency unconverted cavity lacing has been accomplished using a Q- switched Nd:YAG laser as the pump source. The upconversion lacing efficiency was 3.5%, and the cavity lacing lifetime, in terms of pulse numbers, was more than 4 by 104 pulses at 2 Hz repetition rate. By impregnating these dyes into a silica-gel:polymethylmethacrylate (PMMA) and Vycor-PMMA composite glasses, two-photon cavity lacing properties have also been studied.
The performance of a family of rhodamone dyes designed for broadband lasing has been investigated. Conversion efficiencies of 60% and broadband lasing have been attained in this novel class of laser dyes. Lasing occurs in the 570 - 590 nm region with bandwidths twice that of high gain laser dyes such as rhodamine 6G and pyrromethene 580. The lasing characteristics of these stable dyes portends real benefits for the design of wavelength-agile systems.
This paper describes an ongoing study of dye-doped polymer materials as gain media in flashlamp-pumped systems. In this work, we have demonstrated 300 mJ/pulse at 0.4% energy efficiency using PM-597 in modified PMMA. The slope efficiency was maintained at 0.46%, except at the highest input energies. These results are quite comparable to those obtained for the same dye in liquid solution. Two important materials considerations in achieving these results are to keep the bulk transmission losses below 0.5%/cm, and to design the resonator in accord with the static as well as the dynamic lensing of the rod.
This program has produced and demonstrated a small, compact and efficient flashlamp pumped titanium sapphire multiple pass oscillator, that uses a laser head in a close coupled configuration with a single linear flashlamp. This laser has produced up to 1.68 J/pulse in the free-running scheme at repetition rates of up to 10 Hz, with an efficiency of almost 1% at a wavelength of 790 nm. Wavelength tuning from 675 nm to 975 nm has been demonstrated, as having Q-switching, shortening the pulse duration to 20 ns, line narrowing to 2 angstrom and second harmonic generation. An oscillator amplifier configuration has also been demonstrated using a similar arrangement with three flashlamps and two laser rods, producing a beam with energy close to 4 J/pulse.
The research and current state of the art of flash-lamp-pumped Ti:sapphire lasers are reviewed. Further, an overview of present applications of this type of laser is given, presenting in detail multispectral light detecting and ranging (LIDAR) for aerosol size distribution measurement, efficient laser vaporization and short-pulse amplification to high energies. Finally, recent achievements in the field of Ti:sapphire laser technology are presented. The improved design of discharge circuit and pump cavity resulted in increased laser efficiency, average power capability and reliability. Employing a semiconductor switch instead of a thyratron allows for a more compact, reliable and cost-effective set-up of the discharge circuit, which is supposed to meet the stringent requirements for electro-magnetic compatibility (EMC) of the laser systems more easily.
A high-brightness component is used to longitudinally pump Nd:YAG and Nd:YVO4 crystals. The light is focused by a simple, compact and efficient nonimaging concentrator. A 50% at 1.064 micrometer and a 25% at 0.532 micrometer optical-optical efficiencies were demonstrated with a near TEM00 beam.
KTiOPO4 (KTP) has been a frequent choice for second harmonic generation (SHG) of Nd:YAG laser applications. However for high power intracavity frequency doubled Nd:YAG laser systems, we have found it is very difficult to use because of the low damage threshold, smaller acceptance angle and higher birefringence (larger walk-off angle). In order to achieve high power (more than 80 watts) of 532 nm laser light from a single Nd:YAG laser cavity, we have studied the intracavity SHG of lithium triborate (LiB3O5 or LBO), a relatively new nonlinear optical crystal discovered in 1989. Both theoretical and experimental results are discussed in terms of the damage threshold, SHG conversion efficiency, acceptance and walk- off angles, as well as the techniques for both critical and non-critical phase-matching.
Upconversion pumping of Er:YAlO3 in the 800 nm pump band is described. For pumping by cooperative energy transfer, over 160 mW of laser emission at 550 nm was obtained. The pump wavelength was 806.9 nm and the optical conversion efficiency is 17%. For photon avalanche upconversion pumping at 791.3 nm, 33 mW of laser output was produced.
Basic laser performance data for the 4F3/2 - 4I13/2 transition of Nd3+ in phosphate, silicate, and germanate glasses with various doping concentrations are presented. A slope efficiency of 1.1% was achieved in Q-100 phosphate laser glass. The resonator loss analysis indicates that there is no significant excited state absorption at 1.355 micrometer for phosphate glasses. Simultaneous operation of both the 4F3/2 - 4I13/2 and the 4F3/2 - 4I11/2 transitions of Nd3+ in phosphate, silicate, and germanate glasses have been achieved using two different methods. Laser output from these two transitions demonstrate good temporal and spatial overlap under the tested conditions.
A comparative research into the use of Cr4+-doped YAG, YSGG, and LuAG (Lu3Al5O12) as saturable absorbers for the 1.06 micrometer emission of Nd:YAG laser has been conducted. Q-switched pulses with temporal duration ranging from 52 to 23 nsec (FWHM) were observed for the different garnets under investigation. Cross-sections for ground state and excited state absorption were evaluated by fitting our saturation data to Frantz-Nodvik equation. A brief discussion on the use of Cr4+ as a tunable mid-IR laser also is presented.
This paper presents results of a program to develop compact, independently-addressable, pulsed infrared laser arrays useful for applications such as laser topographic mapping. Our approach is based on combining the technology of high-power diode lasers with the recent development of self-Q-switching via saturable absorption in co-doped solid-state laser crystals. Proof-of-concept was demonstrated by the design, construction, and characterization of an independently-addressable, three-element monolithic diode laser array end-pumping a single Cr,Nd:YAG solid-state crystal. Pulse durations of approximately 5 ns at 1.06 micrometer and pulse energies of 8 microjoules at repetition rates up to 400 Hz were obtained with individual pulses exhibiting both excellent repeatability and outstanding spatial mode characteristics.
Using a scalable diode end-pumping technology developed at Lawrence Livermore National Laboratory we have demonstrated a compact Tm:YAG laser capable of generating greater than 50 W of cw 2 micrometer laser output power. The design and operational characteristics of this laser, which was built originally for use in assessing laser surgical techniques, are discussed. The 2 micrometer radiation produced by the 3F4 - 3H6 transition of Tm3+ has many practical applications because it is strongly absorbed by water and also because it is an 'eye-safe' wavelength. The strong absorption of 2 micrometer radiation by water makes this transition a very attractive candidate for performing laser surgical procedures as most tissue types are predominately composed of liquid water. The fact that 2 micrometer radiation is considered 'eye-safe' makes this transition attractive for laser range finding and remote sensing applications where other laser wavelengths could pose a safety hazard. At sufficiently high doping densities, Tm3+ exhibits a beneficial two-for-one quantum pump efficiency enabling well developed AlGaAs laser diode arrays to be used as efficient excitation sources. Many applications requiring 2 micrometer laser radiation such as remote sensing, laser radar, anti sensor, sensor spoofing, and OPO pumping have driven the development of diode pumped all solid state TM3+ laser systems because of their potential for efficiency, compactness, and ruggedness. Here we focus on Tm3+:YAG and the scalable diode end-pumping technology developed at LLNL which enables higher average power operation of diode pumped Tm3+ laser systems than has previously been possible. To date we have demonstrated cw operation of this laser to power levels of 51 W. The end-pumping technology used is the same as was previously used to demonstrate a 100 mJ Q-switched Nd:YLF laser. (Truncated.)
The Nd:GdVO4, Ho:Tm:GdVO4, Tm:GdVO4, Er:GdVO4, Yb:GdVO4 crystals were grown by Czochralski technique. Distribution coefficients of Yb3+, Tm3+, Er3+, Nd3+ ions depend linearly on average radius of a dodecahedral ion. Refractive indices are measured with accuracy within 5 by 10-5 in a range 400 - 1100 nm. Refractive indices depend on the size of the average dodecahedral radius. The thermal conductivity of the doped crystals in the 50 - 300 K temperature range is measured. The thermal conductivity in the <001> crystal direction at a temperature of 300 K is 12.3 W/m by K it is more than thermal conductivity of well-known Nd:YAG laser crystal. As a result of analysis it is shown that vanadate crystals have essential advantages for diode pump lasers in comparison with conventional YAG and YVO4 hosts: large stimulated emission cross section at lasing wavelength; wide absorption band at pump wavelength; low dependency on a pump wavelength and a temperature control of a diode laser; low lasing threshold. For compact design lasers were made crystals with thickness from 2 mm up to 150 micrometers. Microchip laser (monolithic laser) consists of flat-flat cavities formed by a short length of crystal with dielectric cavity mirrors deposited directly on the surfaces.
The neod:yni.iu.-rn-doped la.11.thanu..'n. beryllate (Nd:3+La2Be20 5 or Nd3+EL) laser crystal is biaxial crystal with monocli...'1ic structure. Linearly polarized laser oscillation at 1. 07 and 1. 079 μm are observed. Spectroscopic measurements and a.."'18.lysis ofLD pumped operation ofNd3.,.:BEL crystal at 1.07 μ."'11 (300K0 ) have been performed.The Nd ions doped concentration in BEL host is higher than in YAG over 40% and vithout apparent concentration quench. So, it ca.11 increase the laser efficiency greatly and ca.TJ. decrease laser rod size. For the stronger and broader absorption bandwidth of Nd3+:BEL crystal, it is suitable to LD pumping ..
Key words: laser crystal; biaxial crystal; crystal structure; polarization spectra; LD pump; crystal pulling
Results are presented of an investigation of the lasing characteristics of a high-power neodymium silicate glass spoke-waveguide laser. The influence of short-lived color centers on the lasing properties is investigated. It is shown that short-lived color centers lead to generation of regular giant pulses with repetition frequency up to 30 kHz, to a substantial lengthening of the decay time of the neodymium-ion metastable level (via a decrease of the superluminescence background) and by the same token to an increase of the lasing efficiency. A high-power technological waveguide laser with spokelike active elements, emitting a train of regular giant pulses with total emission energy up to 20 J and high homogeneity of the emission field distribution is developed on the basis of the reported investigations.
The characteristics of a gain-switched tellurite Neodymium-doped glass laser pumped by a Ti:sapphire laser are reported. The slope efficiency is 14.7%. The curves of the dependence of the output laser pulsewidth and delay-time on pump energy are shown. The pulsewidth and delay-time of output pulses versus the different reflectivities of the output couplers are given. The 6.0-ns shortest pulsewidth is obtained.
The absorption spectrum of a new crystal Nd:S-FAP is measured, and its broad absorption band and two strong absorption peaks show that it can be suitably pumped with a tunable dye- laser and a Xenon flash lamp. Using both a tunable dye-laser (570 - 600 nm) and a Xenon flash lamp as pump source, respectively, we have realized the free-running and Q-switched output with BDN dye film at 1.059 micrometer. For the tunable dye-laser pump source, a slope efficiency of 49% and a laser threshold energy of only 2.5 mJ have been measured, while for a Xenon flash lamp pump source, the lowest threshold energy is 150 mJ and the highest slope efficiency is 1.25%. Meanwhile, the emission spectrum, the polarization, the output energy and the pulse width are presented.
The absorption spectrum of a new crystal Nd:Sr6(VO4)3F, known as Nd:S-VAP, is measured and its strong absorption peak at 809 nm shows that it can be suitably pumped by laser-diode. By using a laser-diode pump operating at 809 nm, Nd:S-VAP crystal has been successfully lased at 1.065 micrometer. A highest slope efficiency of 43.5% and a lowest laser threshold of only 11 mW have been measured. The theoretical formulas for threshold power and slope efficiency were written, and the theoretical prediction is in agreement with the experimental result.
The process of the optic pump energy transformation in the system with temperature tuning phase-matching LiNbO3 crystal and LiF:F2+ or F2- wideband laser medium with homogeneous broadening of the amplification band have been investigated. Nonlinear crystal and wideband medium were placed in the common cavity. Excitation threshold of the wideband medium generation is lower than one for parametric generation, that is why generation of the system starts from wideband generation. Wideband radiation seed of the OPO signal wave and excitation threshold of the system reduced. During the generation development, when the system radiates near OPO lines, additional amplification at OPO frequencies brings the effect of condensation wideband spectrum. Wavelength turning in the region 0.8 - 1.1 micrometer was obtained by OPO in the system on the base LiNbO3 and LiF:F2+ crystal in common cavity at 0.532 micrometer pumping. Wavelength turning in the region 1.1 - 1.26 micrometer was obtained by OPO in the system on the base LiNbO3 and LiF:F2+ crystals in common cavity at two-waves pumping (0.532 and 1.064 micrometer). The generation threshold of such a system is essentially less than for OPO on the base LiNbO3 only.
Based on rather simple mathematical calculatioIIB we propose an eftective procedure for optimal cavity design for a 'rariety of laser geometries. Besides the '\lell-kncv.n from the literatlL.re guidelines v..re succeed to perform a forth.er optimization of four -mirror cavity. T:ne possibilities of three- and tvv·on: llrror resonators for building compact Kerr-lens lasers ai.-e considered. Ke)~ords: solid-state lasers, ultra-shOJ.-t pulses, Kerr lens mode-locking, cavity design.
Passive dispersive laser cavity of a new type is suggested and investigated. A distinctive feature of this cavity is the property of rays self-imaging which allows us to ensure spatial separation of the radiation with different wavelengths inside the cavity and creates positive feedback for all the mentioned wavelengths simultaneously. The cavity possesses a number of advantages compared to the resonators with points self-imaging previously developed by the authors and used in polychromatic lasers. A new cavity application allows us to use a wider set of active media in such lasers, simplifies their construction, decreases the demands to the quality of the intracavity elements.
This paper presents results of experimental studies of the spatial profile of the beam in lasers with an antiresonant ring. The near-field profile of the beam was measured by the pin-hole technique. In case of the active crystal placed into the ring, the beam profile was found to be Gaussian within a wide range of the pumping power. Variation of the width of the Gaussian profile is caused by the thermal lens in the active crystal. Measurements of the FWHM of the Gaussian profile demonstrated that it is proportional to the one-fourth power of the focal length of the thermal lens, as in the case of a stable cavity.
Optical absorption, luminescence, kinetics of decay and temperature dependence of luminescence characteristic of Cr3+-doped solid-solutions of gallium and indium oxides were investigated. The single crystals of J3-Ga2-xinx03 solid-solution x=(0-0,2) were grown by floating zone technique using radiation heating. If x increases from 0 to 0,2, interionic distances 0-Ga of gallium octahedron and tetrahedron increase on the average of 1-1,5 % and, as consequence, the position of steep absorption edge of band-to-band electron transitions shifts towards smaller energies approximately by 0,3 eV. Simultaneously the changes of luminescence spectral compositions and luminescence lifetime shortening are observed. When the indium content increases, the R-lines luminescence decreases, but the wide band luminescence from 4T2 levels of Cr3+ -ion increases. The influence of indium oxide concentration on emission, temperature quenching and shortening of luminescence lifetime is interpreted by mutual approaching of 2E and 4T2 levels of Cr3+ -ions. Keywords: oxide, solid-solution, crystal growth, optical properties, absorption, luminescence, kinetics of decay, Cr3+-doped crystals
Radial nonsymmetrical fiber endface microlenses original fabrication technique has been used for high efficient pump laser diode radiation coupling (up to 93% without AR coating) into the standard optical fibers and for the form of a pump power diagram at the output fiber endfaces. Nd:GdVO4 laser (2.5 mm crystals length) parameters with semiconfocal (output mirror curvature radius 10 cm) and monolith plane mirrors cavities have been measured for different pump diagrams formed by plane endfaces, spherical microlenses, and Selfoc lenses. Compact diode-pumped solid state lasers may be used in optical communications, optical storage, medicine, and other applications. Diode laser (DL)-optical fiber coupling gives several advantages for these pumping systems -- a possibility to combine several DLs radiation, a remote DLs mounting, small size and electrical safety of the laser heads, simple schemes of active crystals cooling, axial symmetry of the pumping beam for longitudinal geometry. In general, high coupling efficiency between a semiconductor light source and optical fiber may be achieved by the use of microlens, formed on the endface of the fiber. In this case bulk optical components between DL and optical fiber are not needed. In addition, the only reflection surface exists in this coupling technique. Different techniques for producing microlenses on a fiber endface have been developed. For example, tapered hemispherical lenses, melted, etched, and polished lenses are commonly used for this coupling. However, all types of such techniques produce in general radial symmetry lenses: therefore, they do not provide efficient coupling between a round fiber core and a nonsymmetrical DL's radiation. In this paper we demonstrate the fabrication technique of fiber endface radial nonsymmetrical microlenses with radii curvature from few micrometers to few tens micrometers by grinding/polishing process. This process may be used for producing different nonspherical microlenses (cylindrical, elliptical, hyperbolic, etc.) to efficient coupling DL's radiation into single-mode or multimode optical fibers and for producing microlenses (including spherical) on the output fiber endface to form a diagram of a pumping power.
We present a 'loss balance' criterion to estimate the proper gain medium length (PGML) of the pulsed Ti:Sapphire laser under high pump level and optimal output coupling conditions according to the gain-loss character of pulsed Ti3+:Al2O3 laser longitudinally pumped by a pulsed laser beam, it was proved by several examples, and high efficiency was obtained. In one-longitudinally-pumped Ti3+:sapphire laser, the PGML 1 is determined by the equation: e-(alpha (p)1) plus e-(alpha (p)1/3) equals 1, where (alpha) p is the absorption coefficient to the pump beam, (beta) is the figure of merit (FOM value) of the crystal. When dual-longitudinally- pumped, the PGML is L less than or equal to 2l/3.
The introduction of a 532 nm Nd:YAG beam can be used to increase the slope efficiency of an ultraviolet Ce:LiSAF laser pumped at 266 nm by a factor of 1.4 by bleaching the color centers. The addition of a co-dopant, specifically sodium ions at a concentration of 2% in the melt also increases slope efficiency by a factor of 1.2.
It has been demonstrated that x rays alone can be used to pump a 1061 nm Cr,Nd:GSGG laser. Lasing action has been observed when the laser rod absorbs greater than 27 krad of 2 MeV x rays. The laser cavity consists of a corner cube and an output mirror with a reflectivity of 67%. The x rays are delivered in a 20 ns pulse, and laser action is observed several microseconds after the x ray pulse. This delay suggests that chromium is important in the laser pumping process since it is known that an excited chromium ion takes about 10 microseconds to transfer its energy to a neodymium ion.
The utilization of energy transfer mechanisms to 'down-shift' the high excitation energies of ultraviolet chromophores has significant potential for the improvement of performance of flashlamp-pumped dye lasers. Jones and Rahman (Chem. Phys. Lett. 1992, 200, 241) have demonstrated very efficient fluorescence energy transfer between coumarin laser dyes co- bound to organic polymers in aqueous solution. In the present adaptation of this strategy, dyes have been co-bound by several different means to polymers with varying degrees of energy transfer efficiency. A coumarin (donor) dye has been used to excite pyrromethene (acceptor) laser dyes displaying emission at 560 - 590 nm. Experiments have been performed on (1) combinations of dyes doped into solid poly(methyl methacrylate) (PMMA), (2) a polymer system in which a pyrromethene is covalently attached to the polymer backbone, and (3) dye pairs which are solubilized and co-bound within poly(methacrylic acid) (PMMA), a water- soluble polymer.